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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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84                                 ALASKAN GLACIER STUDIES
stroyed the existing forest and roughened the surface by the introduction of morainic1 knolls since 1890, and that this change had operated not only on the visible piedmont bulb of Galiano Glacier, but also for a distance of four or five miles south of where ice is now visible.
From our study of the photographs of 1890 in comparison with the conditions in 1905 and later years we believe that there has been an advance of the visible front of the piedmont bulb of Galiano Glacier, and a recession of the coast line immediately to the southeast of it; but the photographs were not taken from the right points of view to make it possible to state this as a positive fact.
While there had been such widespread and complete destruction of alder and other growth of vegetation over a wide area, it is a noteworthy fact that the vegetation had again begun to grow on this area in 1905. On the visible piedmont bulb were many individuals and some clusters of young alder, five or six years old, while similar growth, with an abundance of annual and perennial plants, had taken possession of favorable portions of the moraine hillocks that have replaced the alluvial fan. If additional proof were necessary of the recency of the appearance of this morainic surface the condition of the vegetation would furnish it. In this climate, close by the sea, alder, cottonwood and spruce thrive: in fact, they extend even farther up the fiord and also clothe the hill slopes that rise to the west of this area. The morainic soil is unquestionably capable of supporting such growth, for in the interval between 1905 and 1909 the development of the alder has been remarkable. That such vegetation does not already thickly clothe the moraine areas can be accounted for only as a result of the fact, proved by other evidence equally, that the moraine has not been here long enough.
Interpretation of the Changes. These phenomena, which puzzled us greatly in 1905,1 were interpreted in 1906 by the senior author as follows.2 Galiano Glacier possessed features in 1905 not shared by the Black Glacier on the east and the Atrevida Glacier on the west. The puzzling new morauiic hillocks and ridges were concentric and faced Galiano Glacier whose forest had been destroyed since 1890. This destruction followed a long period of stagnation, as shown by the dense alder thicket and forest that grew on the glacier, where we found large broken trunks in 1905, one of which had 75 annual rings. On the border of the alluvial fan, also, quiet conditions had permitted the growth of trees for at least 60 years, and for a long time alluviation had been in progress, building the perfect alluvial fan now destroyed. The abrupt change took place sometime between 1890 and 1905, destroyed the forest on the glacier and for 4 or 5 miles beyond it in the alluvial flat, up through which were pushed a series of hummocks and moraine patches on which vegetation was in 1905 just beginning to grow again. That the change occurred later than 1895 is proved by the Boundary Survey photograph of that year; and that it was not earlier than 1899 is indicated by the age of the new alder plants on the glacier and on the outer moraine hillocks.
To account for this change by mere slumping would involve some special explanation of the 60 or 75 years of immunity from slumping necessitated by the forest and the sudden introduction of excessive slumping over an area of several square miles, and would not explain the broken and splintered tree stubs. Shattering of buried ice by earthquake shaking would share the last disadvantage; furthermore, it would be most remarkable
> Tarr, R. S. and Martin, Lawrence, Bull. Amer. Geog. Soc., Vol. XXXVJJf, 1906, pp. 152-3.
* Tarr, R. S,, The Yakutat Bay Region, Alaska, Professional Paper 64, U. 8. Geol. Survey, 1009, pp. 73-74.